The central theme of the overqall research program is the design, chemical synthesis, characterization, and collaborative application of new probes and reagents designed to overcome some of the currently serious obsticals in biological and medical research. Four subareas form the focus of this five year project. a) New Contrast-Enhancing Agents for Magnetic Resonance Imaging. The long-term objective is to develop improved, clinically acceptable paramagnetic agents that selectively enhance the contrast of targety tissues and organs in MRI appplications. In order to maximize effectiveness of the contrast agent, moleccules to which a larage number of paramagnetic centers may be attached in a chemically well defined manner will be synthesized. The "molecular amplifier" is then attached to the targeting device, e. g., an antibody or liposome, through a chemically reactive arm. Thus, one might be able toachieve excellent contrast with a relatively small number of paramagnetic centers. The amplifier concept is expected to be applicable to other areas, e. g., boron-10 neutron capture therapy. Amplification wil also be sought through the synthesis of highly paramagnetic liposomes and through modification of the "molecular box", apoferritin. b) New ESR Probes for Singlet Oxygen. Singlet ocygen is a likely oxidant associated with the photodynamic effect in biological systems. A water soluble analog of our successful anthracene nitroxide-based ESR singlet oxygen probe is needed and this is our objective. The significance of thes segment is the development of new tools for the study of oxidation, a fundamental process in biological systems. c) New Small, Highly Electron Dense Electron Microscopy Labels. Methods will be developed for the introduction of a radiolabel in our new heteropolytungstate (HPT)-based EM labels, permitting independent quantitation of labeling levels in a biological system. We intend to synthesize a photolabeled, HPT-labeled ATP for a collaborative study aimed at determining the location of the ATP binding sites in F0F1-ATPase, a ubiquitous ATP-synthesizing enzyme. d) Synthesis and Applications of Perdeutero N-Proxyl Nitroxide Spin Labels. With the aim of enhancing the sensitivity of the chemically robust proxyl nitroxide spin labels developed in our laboratory, we intend to develop a convenient synthetic route to perdeutero-15N-proxyls. A chemically well defined spin labeled phosphatidylinositol (PI) as well as a labeled posphonate analog will be synthesized for collaborative biophysical investigation of lipid-protine interactions occurring between PI and membrane proteins associated with membrane recptor transduction.